N-lower alkyl pyrrolidones such as N-methyl-2 pyrrolidone are known as excellent solvents for many polymers. Such lactams are high boiling, have low toxicity and are being extensively used for recovery of polymers such as polymeric residues from equipment such as polymerization reactors. A process for removing polymeric residues from processing equipment using N-methyl pyrrolidone solvent is, for instance, disclosed in U.S. Pat. No. 3,764,384 to Bernie. While the process described in this patent and similar processes are successful, problems have been encountered in separating lactam solvents from polymer residue with the desired efficiency. There is a strong tendency in many such processes for excessive amounts of solvent to be unrecoverable, thus leading to high costs for such cleaning operations. This is due to an increase in viscosity of the solution as solvent is distilled off, thus making it increasingly difficult to remove additional solvent.
It has also been suggested to recover polymer by adding the solvent-polymer solution to water so that the polymer precipitates and then filtering out the precipitate and removing the water. While theoretically attractive, this is impractical on a large scale because of the large volumes of water necessary to obtain adequate precipitation of polymer.